This invention concerns self-steering railway trucks wherein the wheel sets are able to assume a radial orientation with respect to the center of curvature of a curved track section being traversed thereby.
Conventional three-piece railway truck designs comprised of a pair of laterally spaced side frames and a bolster extending transversely therebetween have become the standard in many railway industry applications; however, in many conventional truck designs utilized in conjunction with conventional track layouts and wheel conics, the wheel sets may not track radially around curves but instead may tend to slide during negotation of track curves. Additional problems encountered with conventional trucks include the tendency for the wheel sets to traverse curves in a non-radial orientation and with much wheel flange-to-rail rubbing contact. Such rubbing contact and wheel sliding result in undesirably high wheel and rail wear, and the flange rubbing in particular may produce a tendency for the wheel to climb the rail and cause a derailment. In addition, improper wheel set tracking in curves may result in track misalignment.
Other related problems occur when conventional trucks traverse straight or tangent runs of track. For example, a rigid wheel-axis set, having conventional tapered conical wheels, when displaced laterally of the center line of a run of straight track, executes two simultaneous motions; first, the wheel set moves toward its equilibrium (centered) position under the influence of gravity, and secondly, the high side wheel, rolling on a larger diameter than the low side wheel, moves along the rail faster than its partner, causing the wheel set to yaw. Given the proper set of conditions, this motion may become a sustained harmonic oscillation known as hunting with the sinusoidal peaks being clipped by contact between the rail and the wheel flange.
When rigid wheel sets are coupled in a truck through the side frames, or rigid truck frames, the hunting tendency is transmitted to the truck and causes an oscillatory yawing motion of the truck about its center of rotation. Continuous or semi-continuous motion of this nature is transmitted to the car body which then yaws about its center of gravity, or about the center plate of its second truck if that truck is not hunting.
Railway rolling stock design has been evolving toward higher center of gravity cars, heavier loads and higher operating speeds, all of which have the potential to seriously aggravate the problems described hereinabove. These problems have been recognized in the prior art with the resultant development of a variety of self-steering railway truck designs which purport to allow the wheel sets to track without sliding and without undue flange rubbing during negotiation of curves, and with minimal adverse consequences resulting from hunting.
Considerable prior work has been done in the area of self-steering railway trucks; nevertheless, there has been no overwhelming commercial acceptance of any self-steering railway trucks heretofore even though a significant need exists in the industry. The apparent reasons for industry non-acceptance of prior self-steering trucks include their relatively complex designs with resultant operational and maintenance problems; inherent requirements for substantially new truck designs; the inability to readily retrofit and/or to conform to inherent space limitations; and limitations in designs which provide for steering but which, in turn, amplify the tendency of the railway car to hunt in unloaded conditions on straight track to an unacceptable degree or to a degree that control thereof is uneconomical or unfeasible.